This application i' a continuation in part my copcnding applications :r..tl No. 4l,533. filcd July 30, l948; Serial No. 370,415 a: ll Serial No. 422.096. nc'w all abandoncd. The said ro-ponding applications mainly claim "various features of the product and methods of manufatturc.

l have dis-covered tnnt expanded pcrlite even hen as finc as that used in the illu trative products of this and the-above parent applications is very t'rrc filtering, that is, it tle-waters quickly. This is intrortnnt in the illustrative method of making the product wherein the solids are dispcrscd in an aqueous slurry of pcurable ccusistcncy (though of vastly greater concentration than conventional fiber siurrics used in the manufacture of fiber board and 1h:- likc) and then formed and tic-Watered. Suzh a slurry may b: very rapidly de-zvatercd as compared with the time required to dc-watcr the fiber slurr (with or without other aggregates or fillers) heretoftrc used for the forming of fiber board. This is a proprrty peculiar to pcr'zitc as compared with other insulating aggregates such, for example as exfoliated vermiculite whim is very slow filtcring (regardless cf particle sizt) due to the multitude of contacting fiat faces and lamina characteristic of carfoli'ltcd vermiculite. As stnlcd above, the product is essenticlly a mass of expand-d pcrlitc particlcs contacting each other only in limited areas sulficent to prove shrinkage yet leaving the mass "open" to receive the fibe network or skeleton without impairing rapid dc-wvhrin". The amount of fiber used is generally small compared to tho large volume of pcrlite (one illustrative volumetric rat o being about 5 or 7 of pcrlilc to l of fiber).

Preferably, the proportion of fiber is limited to what is cccssary to give adcouatc strength to the product, because additional fiber would unnecessarily reduce the deateriug or filtering rate. Since the fibcrs lie mainly in the interstices between the granules of :mrI-ite, the fiber docs not substantially increase the volum; o the product over what it would be with no fiber added. ln on: type of expanded pcrliic granules of which abott 70% are minus 16 and plus 50 mesh. about 48% of t: .otal volume comprises voids between the granules. This means that fiber equitalent to about 48% of thc tota voume of the pcrlite might be added without increasing the volume of the final product over that determined by the pcrlitc alone. Actually, of course such a high amount of fiber is not only unnecessary but actually obiectional.

The significance of avoiding increase in volume over that determined by the pcrlite alone is this: If so much .tli': fibers may lie without incre fibcr were added as to caus: inzrcsse in volume over that of the 'perlite \sithost fiber, tlur: would be substantial shrinkage of the product cn drying. Shrinkage is c aiously objectionable; A mass of pxlit: alone does not substantially shrink on drying because thc granule-s of palilc are in substantial contact vsith 2:,- surrcunding granules and since they act as though they crc gccerzliy spherical in charactcr, they protiie intersticcs in with g the volume of the mass over that of thc pcrlitc alcnc. and drying out of the water held by tho fibers does not, tbcrcforc. result izi shrinkage of th: 'trctluct. .111: mm generally spheri is employed to describe the nature of the contacts between granules rather .lnn their literal shape. L11: sphcrcs. they contact in points rathcr than in surfaces v.hcrein capillarity would operate to hold water and thereby resist dc-wntcring; and like spheres they prosi c spaces where fibers may lie without increasing the volrzs: of the mass of granules alone. Axually, the grass. may have (but not always numrvus points proiec'ing from them (cal ed rabbit vars" in the trade) uhich have the same effect as spherical aortas-5,05 limiting courses to points rather than surfaces. v

The fibers. on the other hand, zr mainuined by 73;: pcrlitc particles in the form. of an opcr: net work and held against segregation which would retard d-wston'zg. The pcrlite particles provide such a fine grained teams: as to leave no large voids where a substantial large urnher of fibers may collect 811i b!oclc the void: and interfere with rapid tie-watering. The open tex ure of the 55::- nct work maintained by the perlitc and substantial absccca of bunching or segregation of the fibers, is further r:- veriled by inability of the livers to retain or hold a. substantial amount of water during the (lo-watering prccsszs, as compared with products in which a substantial number of fibers are close together. The product may, therefore, be tie-watered to what is termsd a dry condition, lea'dcg much less water to be remo ed by drying vn'th heat.

Except for the foregoing considerations and those out enumerated, the fiber may be varied from the above H trated ratios. if increased, it provides some increase in strength but with sacrifice -f izsulating efficiency. nonoombustibility and rapid d-a-watcring properties and increase in cost. For example, if the product has as high as 30% by weight of vegetable fiber (such as newsprint) it begins to lose some of its rapid tie-watering specd. With 20% by weight of newsprint. Lbs product has ade quate strength, i.e., a modulus of rupture of 45 pounds per square inch.

Ratios by weight between the fiber and perlite vary with the nature and density of the fiber. The contro ling relationship is actually the ratio between numbers of individual fibers and the numbers of particles of fine perlite, but there is no practical way of counting either numbers of fibsr or pcrlite par icles. Hence, in doscribing the invention the ratio can be has: expressed either by volume, or preferably by weight for each specific fiber or other variable constituents. The preferred ratio (fiber to perlitc) by weight of newsprint and similar wood or vegetable fiber is about 20-30 parts by weight of fiber to 70-80 parts by weight of pcrlitc, but for the same number of commercial asbestos fibers (for exam plc) as paper fiber, the weight of the asbestos fiber would be'much greater because asbestos has a high specific gra'ri ty and it is not practically possible to sub-divide asbcstos into its ultirF-ate fibers, a fiber actually comprising a bundle of fibers. Commercial asbestos fiber has a specific gravity of about 2.5 whereas paper or wood.

fiber has a specific gravity of .6 to .7. Therefore a given number (or volume) of absestos fibers is very substantially heavier (about 4 times) than the same number Percent Perlite 60 Asbestos fiber 30 Kraft fiber 10 the ratio of the several constituents by volume is approximately Percent Perlite 93.33 Asbestos fiber 5.34 Kraft fiber 3.23

if the total volume of the product (including the voids between the perlite granules, about 48%) were considered, the volumetric ratio of fiber to pcrlite would be still lower.

The above volumetric relationships demonstrate that the product is essentially perlite and not fiber adulterated with perite. Further, the circumstance that the product will not support corhbustiorl (even though all the fiber be vegetable) demonstrates how well the fibers are separated or isolated from each other, and how small the proportion of fiber actually is.

The illustrative product may be made from perlite ore which is preferably too fine for use for plaster and concrete aggregates. Such ore is generally from minus 50 to plus 100 mesh, which results in a high percentage of expanded perlite which should preferably not be used in plaster or concrete aggregates. However, the product is not limited to particular ore sizes or to a specific range of sizes of the expanded pcrlite granules, except preferably not more than 2 to 5 percent should be finer than 325 mesh (ie. 44 microns) and preferably not more than 20% should be larger than 8 mesh. However, large granule sizes, assuming that there be an adequate range of smal!cr sizes, are objectionable only to the extent that they may tend to fioat to the top in an aqueous slurry and thereby segregate. The present process, hereir fter dcscribcd, is adaptable for use with crude perli cs, but in expanded form in a. wide variety of classifications or grade: of crudes. The particular grade of crude perlite ore, as mined, often determines the particular grade of exparded pcrlite available for the manufacture of the instant board. The following grades of pcrlitic ore and expanded perlitc are adaptable, for example, for use in the manufacture of insulating products according to the present process:

(4) Expanded perlite, the major portion of which passes a 20 mesh screen and finer with a substantial portion 100 mesh, and

(5) Expanded perlite, the major portion mesh and finer with a substantial portion 100 mesh.

It is possible to effect a m'utture or selection of various grades, utilizing particularly those rades not suitable glass, as'c for the cnzzufacture of other tTQdUCiS, iQ tL{If-Pl, aster concrete a crecategt. The following ear andcd 5' gs are'a.so sortable for use in the instant anufactuting the board of this invention:

Generally speaking. the expanded pcrlite used for the manufacture of the insu.aling board of this invention should be of a. grade such that a major portion, or at least a substantial portion be capable of passing through a 20 me h screen and a substantial portion be of approximately mesh grade or finer.

The term pcxiite is used herein in a generic sense to include pcriite and perlitic vesiculating materials generally.

To distribute the relatively small amount of fiber uniformly tlt' "bout the large bulk of expanded pcrlite particles, :t fiber such as newsprint or other relatively short veg le or mineral fiber (cg. glass wool, fiber cs) is preferably used. Newsprint fiber (which F E: advantage of relatively low cost) has an average of about with a maximum length of A", \vhcrc lLraft fiber (which may also be used, though it is more expensive) has an average fiber length of about I /4 to 5's" Asbestos fiber of jD Canadian grading is short enoue': so that about 'd'ifill p 55 tbm lgh,.a.c4.,xnesh screen and :1. c retained oh a ntcshscrcen. Whi e M sMwWw =21: of long hoer (vegetable or mineral) can a sma araalso be d5 atcd throughout the perlite, it is dimcult to substitute fiber (despite the advantage of its greater strength) e 'cly for the short fiber. Long fiber bunches if it be p in any substantial amount, and thereby takes di. uniform distribution of it throughout the slurry.

To obtain strengths comparable to what would be obtained if long fiber could be used substantially exclusively, the short fiber is preferably trreatcd to increase its mutual friction or tack by applying thereto a relatively mall amount of a non-migrating friction increasing substance disp ible in water. In the illustrative method such substance is preferably added to the aqueous slurry containing the fiber in the form of an emulsion or dispersion to permit distribution of the relatively small amount over the relatively large surface of the fiber. It tends to coilect on the fibers rather than on the perlite particles. For convenience such substances will be referred to herein as a tack material or substance adhesive, or bi-.;er. It should preferably be non-migrating so that it will remain on the fibers and not travel to the surface with the water as it is removed from the product or concentrate in the surface of the product on drying. This excludes most true solution even though they have tacky characteristics. For most products migration of the tack substance to and concentration in the surface layer of the product, is not desired, though where a very strong and tough surface layer is desired, some migration may be perrritted. In most such cases, the interior of the product would be correspondingly weaker.

It is believed that the adhesive in crcases the friction bewfibcrs an ance to being pulled nded perlite, 59% of which is plus 65 mesh as fillers. While it is believed that the adhesive sabstance board also has the appearance of a board coczairiag fiher and perlite held together by a binder. As a result. while it is believed that a tacking action between the fibers and the adhesive occurs and very little tacking takes place between the perlite and adhesive, for the pur -axes of this invention the adhesive may also be considered as a binder.

In general and independently of the specific fiber and taclt substance used, the ingredients of which 1!..- board is comprised should be present in amountwt in accordance with the following approximate percentage ranges: eztpanded p-r 22-10% and a MMM' 3 for most commercially attractive products not more than apprcximately and not less Lnan approximately 5'2: for most products best exemplifying the invention. Preferably. an approximate general formula by dry weight for a finished insulating andacoustical product lite articles 0' fibers, estve or hinder. up to apptcximatly is: Y Percent Perlite 7O Fiber 15- 30 Tacit substance l0-25 To avoid too low a strength, the ratio by i fiber to pcrlite should preferably not be subs: ly less than t to 4%. A ratio by weight of fiber to perlite of about 1 to 3 is preferred. In terms of weight of the product made with vegetable fiber, this is aboct 2 3% fi her and 60 to perlite, the balance belie tzcl; substance. For other fibers the weight may vary tly d5? pending on the characteristics, length, weight and strength of the fiber. Insulating board of this character should not weigh substantially more than 8 to 10 pounds per cubic 'foot; but if a tougher and stronger board be necessary weights may be increased to 15 pounds per co'cf: foot by greater compression of the board during manufacture.

The concentration of solids in the slurry used in the illustrative method depends somewhat on the rzethod of manufacture. When the product is formed on a cylinder machine or Fourdrinier, the concentration of solids may be 3 to 8% to make a product having a dry thckness of at least one inch. High rather than low conceczation of solids is preferred both to increase production and to combat any tendency of the larger particles of expanded pcrlite to rise in the slurry. This contrasts with the dilute slurries used in the manufacture of conventional fiber board and paper in which the solids cannot exceed .02 to .5%. When formed in a suction mold the concentration of solids in the slurry may be much higher than for a cylinder or Fourdrinier machine. Regardless of the method of formation, de-watering is very rapid due to the "open" nature of the mass of perlite particles and ab sence of fiber bunching or segregation.

After and during forming, the board is lighzly compressed to give it uniform thickness and to consolidate it. The-residual moisture (remaining after application of suction and pressing) is preferably driven out by heat to accelerate drying.

Whether the board is dried in a continuous web or cut in pieces before drying, depends on the type of apparatus. Generally it is preferable to cut the web transversely at intervals before entry into the drier. The dried board is then trimmed to size; and if it be intended for use as an acoustical material, the face'of :..e material may be drilled to provide conventional sound receiving recesses, or a thin layer may be cut from the surface if it be desired to increase the porosity of the surface for sound atseew' om- For other uses, surface cutting would be' undeslrzble.

Various binder, tack or friction increasing substances may be used, deprndiag somewhat on the uses and desired propcrties of the product. In my said co-pending applications, bituminous :zzulsions, sodium silicate, pitch.

' bentonitc, and various resins and dispersions of starch and cements are discloses. Light colored tack substances, such as sodium silicate. sczrch and light cofored cements and resinemtsiorts cfszspensions are preferred for an acoustical or sound inst-.LLi'c-n since they would not bleed through or discolor the :azerial ifpainted. Emulsitied asphalt has the advantage of low cost and it gives the product excellent water rzcerlency, and, surp s ngly, the product will not support. combustion. At very high tem-' another. The same apples to other organic tack substances such as starch and resins disclosed in said cope tding applications.

The invention is not [Liaiied to the specific taelrsub stances enumerated, bu considerations ofova-liability,-

cost, etc., practically lir them to tack snbszanzes which are low in'eost and (s im-n the illustrative method of manufacture is used) are readily dispcrsible in an aqueous slurry. Other solvehtsec liquid phases for the tze-l; substances are costly and :23 be more ditiicult to disperse in water, and they may also involve a fire hazard in manufacture. Aside from the matter of relatively high cost, synthetic resins cc-i-d be employed. One example is calcium acrylate, a W11. soluble monomer which be comes water insoluble. :1 general, however, water solutions tend to migratetc icsutfaceon dryin and tend,

to concentrate the tack substance in the surface. This is characteristic of mes: soluble tack substances, and it has been regarded as true of sodium silicate.

W has s e use a ,t.,? "og cmflfs' t't's j'fi' an dhesive has h---tnforc ic-cc: limited 0 t oducts in which migration of the so tta concentration in the surface layer of the product...

has not-been objectionable. For example, sodium silicate uscd tg bond etfi a ted vermiculite in a molded or otherwise form'd' pro cactfbitt on drying, the water therein or: escaping to "'2 surface carries a substantial amount of the silicate to the surface where it is left as the water evaporates. Tia: surf ace layer of such a product is quite strong and dense cut if it be trimmed off for any reason the remainder of the product, having little silicate to bond it, is very weak- Also, in other products, sodium silicate has been vulnerable to the presence of moisture and is not regarded as W222. resistant. For these reasons,

although its adhesive pfapertici gtrg gggllg,Otfii4tn silimehas'hgtfgg' f da satisfactory fut products ammonia -tteirtanse sunrise" is as tionable or where it may be exposed to moisture.

I have; discovered the; contrary to all $91155}- perience in the use of t e s 'n-n srl ate does not substantially 029215512 y n- 'a'- t the su ace in the present ccluct ygich comprises mainly emillgwrlitg I beli e is du'tarasnsrdrme sodium silicate with the perlite itself which is an aluminum s licate. My presezs theory is that the reaction between the perlite and ti: sodium silicate increases the viscosity of the latter or-oincrwise changes'its nature so that it migrates less Sodium silicate does re aet with glass, Among the evidences tmreaction does take p ace bet can the sodium pcrlite and the -.'eg:table fiber silicate and pet-lite, is the circumstance that it pure sodium silicate solution be passed through a body of expanded periitc, an aluminum silicate is found in the filtrate. Aluminum silicate is a very refractory bonding agent. Furthermore, increase in the soda to silica mtio (which might occur in such reac ion) increases the viscosity of the sodium silicate, thereby reducing its tendency to migrate on drying out of the water. Also, the fact thct in some cases perlitc acts as a catalyst may explain the unexpected impairment of its tendency to migrate. Other aggregates do not thus affect sodium silicate. For example, if exfoliated vermiculite be substituted (in identical volume) for the perlite in the illustrative product, with In) other change, the sodium silicate will migrate so substantially that the modulus of rupture of the center 1" core of a 3" thick slab is rcluccd by 40% over the strength of the remaining outer 1" thick pieces of identical dimension. ln :1 similar pcrlite slab, there is only a sm.-.ll difference in the modulus of rupture between the center core of the slab and the remaining pieces, indicating some, though small, migration.

Another indication of a change m the nature of the sodium silicate in association with expanded pcrlitc, is the unexpected resistance to dis ntegration of the illustrative product under prolonged soaking in water. So.;king in watcr'for over a month, while softening the product somewhat, did not result in disintegration. After drying, the product retained 75% of its original strength. in otherwise identical p oducts wherein exfoliated vermiculite rcplcced the expanded pcrliic, complete disintcgration occurred after soaking for 72 hours. As a bending agent, sodium silicate has been notoriously vulnerable to moisture. Its unexpected resistance thereto in association with A product of this character wiil withstand the severe fire tests specified in Federal Specifications SSA-l18a, which comprises exposure of a 9 square foot area of the product for 40 minutes to an impinging flame which raises the tempczature from room temperature to 1700 degrees F. in 25 minutes and then holds. the temperature between 1700 dc grees F. and 1706 degrees F. for the remainder (15 minutcs) of the test without substantial falling apart of the roduct. The continuous glass reinforcement formed by \the sodium silicate, even though the fibcr be charred,

prevents disintegration of the product under such heat. As stated above, the fiber (if it be vegetable fiber) is too isolated and is present in too small an amount to assist in propagation of flame or ccmbustion throughout the product. The very large proportion of periitc acts as a barrier to propagation of combustion aiong the ft'ccrs. The depth of pcnetr'iion f the charting emperatures above defined, does not exceed about A inch. Of course, non-combustible fibers such as glass fiber, asbestos etc., may be used, particularly if the product be teaded for t tem eratures which would m lLqg buto erwis c c a -C! *r suc as newsprint or Kraft is preferable from the standpoint of ost and ease of distributi'm taroughout the slurry.

The aforesaid tata; su'astances while contribu ing differont incidental properties to the proclact, are believed to have the common characteristic of inzreasing the tack or mutual friction between the fibers, increasing their resistance to pulling apart and giving the oduct a strength {equivalent to that theoretically ohtainablcwith long fiber, iii the latter could be uniformlv distributed throughout the product, and of etiecting a binding action to coat :inc and 23 for manufacture of a product of this character.

As stated in my co-pcnding application Serial No.' 45.533, dilution with water beyond what is necessary to :21: g pourable slurry, is prcfcrably avoided. Even v-EL': such an abnormally high concentration of solids t'c: illustrative products may be readily made to dry thickncsacs of l" and more without difficulty. indeed, the

'ation on thicltncss is not dct:rmincd b the time req d for dcwatcring (because even thicker material may be quickly dcuatcrcd) but by that 'licilrtcss which may be 2105! rapidly dried in the drier after tie-watering, material thicker than 1" requiring more than a proportionally -lo:c;r time to dry. it is preferable, theref re, to orm the cm: s not substantially thicker than 1" to obtain the most F 'cnt drying and if a thicker board he desired pluof boards mav be cemented together to obtain the desired thickness.

Gcncraliy, the board comes from the de-watcring step so dC-WulC-Cd that it is termed dry" (though it is not .ally dry) and needs little or no pressing before it enthe drier. Gcmrally, a single pair of pressing rolls cs. -Howcvcr,'it should be'ier'ncmbcrcd thatthe suc- 02 used in de-wctcring causes compression of the board to $3.. 2 extent through the action of atmospheric press'cL-c.

01' course, an even greater concentration of solids may be z'ohncd and deuvatcrcd in simple suction molds, but

$1.: methods of formation are slow as compared with fermion by a cylinder or Fourdrinier machine.

Tani: the low fiber content which characterizes the prznt product. strength varies with the proportion of a- 3: no more fiber is used than is necessary to hold the per- .n its formed shape. If the fiber c ntent be increased, tack substance should also proportionately inthe cre Laizza ie from the increased proportion of fiber. Within lir ts, depending on the nroPortion, length and strength of the fiber, strength can also be increased by increasing thc foot) 7 Fi er (pulpcd newsprint) 20 Asphalt (used in the form of an emulsion containing -f=360% asphalt) 10 Example No. 2

- The sodium silicate employed was 6 to P-. coneentra l tion wl'h a soda to silica ratio of l to 3.36. Although the raft titer chars at the temperatures to which a board of this character is exposed, it provides a good wet strength during manufac u e. i Other examples are described in detail in said co-pcnding application Serial No. 41,533.

it the tan color resulting from the us: 02 asphalt as a tack material be objectionable for any reason, as in an acoustical insulation, light colcrcd tack substances such as sodium silicate and those disclosed in said two-pending application Serial No. 370,415 may be used. One material using starch as a tack substance comprises:

Example N0. 9 Percent by weight 25 Expanded perlite Fiber Cooked starch 10 The above product weighs 6% to 7% pounds per cubic foot and has a modulus of rupture of 50 to 60 pounds per square inch. Roughly, the ratio 'of starch to fiber is about 0.4 of a poundof's'tarch per pound of fiber; while as little as 5% .of cooked starch may be used. bezcer strengths are obtained with 10%.

Other examples using starch are as foilyas:

The starch gives unexpected water resistance: Prolom edsoaking'of the product in water for three weeks resultsin only slightly. softening of the metric]. Greater water resistance may be obtained by the addition of a water repellent material such as a resin emulsion. Additional water repellent substance used for an acoustical COltl'd should, of course, be limited to a material which will not obiectionablydiscolor the board. One suitable 50 waterrcpellent substance is an aqueous emulsion of a ln addition to its advantages in a product subject to high temperatures sodium silicate, because of itsdightcolor may also be advantageously used as a tack sub- 55 stance in acoustical installation.

. A third product employing a sodium silicate solution of minimum concentration (4 degrees 8:. solution) com- Such a product has a modulus of rupture of 61.11 pounds per square inch, :1 weight of 7.86 pounds per "0 cubic foot but failed, after 18 minutes exposure to the tire test. While the latter strength would be sufficient for rut-acoustical insulation, if the board were not superficially trimmed, such a low concentration of sodium silicate results in some migration to the surface with the result that if superficially trimmed, to expose the maximum open pores the strength would be less.

Another product embodying asbestos fiber with sodium silicate as a tack substance comprises:

Example No. 17 Percent by weight Pe'rlite 48 Asbestos (5D) fiber 24 Kraft fiber 8 Sodium silicate .The expression 5D above is a Canadian standard classification for an appropriate type of commercial asbestos which generally identifies the character of fiber by fiber Perlite 4 Asbestos fiber Kraft fiber l0 Proportions ofthe several constituents may be varied considerably in relation to each other, but for products having generally the physical properties of those given above, the constituents should preferably not vary substantially more than the following: Pcrlite 5% above or below that given above; ltraft fiber not substantially more than 2% above and below; and sodium silicate not more than 4% above and below. The asbestos fiber may vary between l5 and However, to obtain the advantages which should ensue with an increase, for example, in

--fiber,- the tack substance should also be increased and vice versa. For, in order to obtain the increase in strength which additional fiber should provide, there must be an increase in tack substance. On the other hand if the fiber be reduced, the tack substance can be correspondingly'reduced without causing additional loss in strength.

Considering the various practical uses of the product and the strengths desired for such uses, a 10 degree B.

strength necessary for the major types of uses and a great surplus of strength for many uses. Such a coneentraticn. using the same ratio of fiber to perliteas above, results in 23% of solid sodium silicate in the product. Besides providing adequate strength, if the prod ttct be exposed to fire, enough sodium silicate is in the product to form the supp ementary reenforcing glass dc veloped on exposure to tire. Aside from the matter of increase in cost resulting from increasing amount of sodium silicate, too much sodium silicate is not desirable in products designed for maximum resistance to fire because too large an amount of fluxed class in the product. may cause high internal stress, resulting in warping or cracking of the product on cooling.

While there are various grades of sodium silicate (varying in their soda to silica ratio) the least expensive commercial grade (having a soda to silica ratio of l to 3.36) is satisfactory.

Except for high temperature thermal insulation (i.e. temperatures of 300 degrees F. and higher) and products in which vegetable fiber is objectionable for other reasons, vegetable fiber is preferably used both because of low cost and because it facilitates manufacture by low curt methods. For temperatures of 600 degrees F. to 1200 degrees F. encountered in industrial insulation such as pipe coverings, it may be desirable to replace part or all of the vegetable fiber with mineral fiber such as asbestos and glass fiber. Preferably some vegetable fiber is used to git: increased wet strength. In products of this character sodium silicate is preferable as a tack material.

Between 300 degrees F. and 600 degrees F., vegetable fiber can be used if there be no objection to slight local or superficial charring in the regions where the higher temperatures are encountered.

While the product might be made by other methods than the above described slurry method, these are re-v garded as less economical. Substantial and unexpected advantages accrue from manufacture on a Fourdrinier machine: (1) the stock or furnish may be more concentrated, as high as 8% solids, an unbelievably high concentration, the limitation on concentration being not the difiiculty of de-watering, but the flowability of the furnish, with higher solids-concentration, the furnish might not flow with sullicicnt readiness; (2) because of the high solids Concentration, larger perlite particles can be included than could be used in a less concentrated furnish because of their tendency to float to the surface; and (3) an opportunity is afforded for removal of a sub stantial amount of water by natural drainage while the board is on the wire and before it reaches the suction boxes.

To make a 1" thick finished product, the furnish is flowed onto the wire (which is a foramincus surface) at about 2 /1" in thickness. Even before reaching the suction boxes (a distance of about 20 feet, traveling as fast as 9 feet per minute) it has de-watered itself by natural drain ge (i.e. without suction) to a point where it is practically self-sustaining (i.e. dccklc boards are no longer required .0 maintain the margins of the wet board). In passing over the suction boxes and under the pressure and gauge rolls (but'before passing into the driers), the material comes down to about I" in thickness (e.g. about 1.04). In the drier it shrinks about 3 5 in thickness. Absence of substantial shrinkage is due, as stated above, to the circumstances that the product is substantially entirely perlite particles in contact and that the fibers lie in the spaces between the contacting perlite particles.

If due to the high concentration of solids, the surface texture of the stock as it lies on the Fcurdrinier wire, is rough, this roughness may he completely removed and a perfectly smooth top SJIfaCC produced by gentle puddling of ti surface of the stock on the wire before it rea:hes tl'e suction boxes.

In mixing up the furnisl' i is advantageous to add the earpzzied perlite to a slurry conLaining the fiber (an aque- :11" of about 1.5 to 2.5% fiber concentration) with an 2;:113 anion so that the perlite particles are fully ier d. For example, the perlite may be added to a whi lpool or vertex of the ficer stock which feeds into the bead box containing the comentional agitator and feeder. The tack substance (e.g. emulsified asphalt, so-

d3::t s-l cate; etc.) may also be added to the vortex to be t3:-rc;hly distributed throughout the furnish.

As stz'eed above, the unique chzracteristics of the expzrrded perlite make possible the h gh concentration of solids in Le furnish, the high proportion of perlite in the prcirart, and the ready de-watering and great thickness :1 the board may be manufactured and the high speed of formation.

Ob-Iously the invention is not limited to the details of the illustrative embodiments thereof since these may be .-.rIo modified. Moreover it is not indispensable that all features of the invention be used co-iointly since va ious features may be used to advantage in different ons and sub-combinations.

described my invention I claim:

'ng essentially of about sixty percent by weight .0 of in: particle of expanded perlite substantially none of posited on the exterior of the fi'rers but being insufficient in amount to bond the fibers.

2. article of manufacture, an insulating material essentially of particles of expanded perlitc held ed form by a network of short fiber substantially v distributed throughout the mass of perlite, the '12 of 65 mesh and finer particle size with a 1 proportion as fine as 100 mesh, said perlite 3 not less than about 60% of the dry weight of the prcxiect, the fiber comprising not more than about 207: of t. -e dry weight of the product and having on its surfaces not more than about of the dry weight of the product of bituminous adhesive substance which increases the mutual friction between the fibers to give the product a strength analogous to that which would be obtainzble from long fibers.

3. A thermal insulation consisting essentially of not less than about by weight of fine particles of expanded pzrlize of 20 mesh and finer particle size with a substantial proportion as fine as mesh, said perlite being held in the form of a substantially thick sheet by a network of short fiber comprising not more than about 20% by weight of the dry ingredients, the volumetric ratio of p..rlite to fiber being not less than about 5:1, the fiber befsg substantially uniformly distributed in the mass of per i: but being too short themselves to provide adeq ate strength, and an amount not exceeding about 20% of the dry weight of the product of bitumino s adhesive substance on the exterior surfaces of the fibers to increaw the mutual friction between the fibers to proside adequate strength.

4. The method of making a substantially thick insula- Lion board or the like utilizing a continuously moving for-.minous surface which comprises forming, with mixing. an aqueous slurry of pourable consistency and containing about sea-3% by weight solids consistingcessentially of (l) expanded perlite substantially none of which is larger than 20 mesh with a substantial proportion as fine as 100 mesh, (2) fiber, and (3) a small amount not exceeding approximately 25% or the dry weight of the product of a non-migrating adhesive substance, the volume of perlite being at least 5-7 times that of the fiber and the fiber being short so that during mixing the fiber may be unil. A th=rrnal insulation molded from an aqueous slurry -5. The method or making a thick fibrous board. or the like. on a foraminous support which comprises making an aqueous slurry having a solids content consisting essen tially of approximately tl) sen expanded perlite, (2) 20% newsprint, and (3) 20'? emulsified asphalt, the concentration of solids in said slurry being not less than approximately 3% by weight but no: greater than approximately 8% by weight. forming on said fornminous sup-- port a relatively thick layer froaa'such slurry of such thickness that when dry the product will not be substantially less than one inch in thickness. dewatering said layer by removing the water through said support until the particles of perlite are in subszanziai contact with each other, and drying said layer to remove residual moisture.

6. the l'l'lclhOt! of manufacturing a fiberperlite board comprising the steps of forming a slurry consisting essentially of fibers, expanded perlite particles, water repellent organic blindcr and water, said s'urry having a solids consistency in the approximate r' go of 2.872-89'6. by

weight, said expanded perlite compri ing about 60%-80% of the dry weight of the formed board, said fibers comprising about 3595-1555 of the e'ryweight of the formed board, and said binder eompr zg a substantial portion of the dry weight of the formed cs-ard, conzinuousiy forming a we: mat of said solids and draining the water therefrom, and removing the reside-ti moisture in the mat.

7. The method of forming weight insulating material utilizing perlite containing a substantial portion of particles as small as 100 mesh, comprising making an aqueous slurry having a solids content consisting essentially of perlite, short fiber, and water repellent organic binder, the ratio by weight of per-51c to fiber being at least approximately 3;! and the amount or water being sufficient to form a slurry having a concentration of solids in the range of approximately 55 .45% by weight, mixing the slurry to secure uniform distribution of the fiber throughout the perlite, placing the slurry upon a foraminous surfaze to permit the water so drain from the solids deposited thereupon and the fibers to lie in the interstices between the perlite particles and be held thereby against segregation during draining oz? of the water, and removing the residual water by drying to render the binder efiective.

8. The method of manufacturing a fibrous pcrlitic board comprising the steps of forming a slurry comprising fiber, water, and water repellent binder, adding expanded perlite thereto so as o form a slurry having a soiids consistency in he range of approximately Mir-8% by weight, the approximate ranges of percentages of the solid ingredients being BYE-15% fiber, 60%-80%' ex panded perlite, and Sk-lO'iE biaderby weight of the solids of the ultimately formed dry board, most of said perlite particles being capable of passing a 20 mesh screen, transferring said solids in the slurry to a continuously moving foraminous support to form a mat thereon, and removing the moisture contained in said mat.

9. The method of manufacturing a fibrous-perlite board comprising the steps of forming a slurry consisting esssentially of fibers, expanded perli:e particles, asphalt and water, the solids content of said siurry being in the ap -roxim'ate range of 2.8924; by weight, a maior po'r-.

tion of said perlite particles being of a size to pass a 20 mesh screen, said perlite particles comprising about 60%- 8055 by weight of the resultant relatively dry board and the fiber particles comprising about 3595-159? by weight of the resultant dry board, ccnzinually transferring the slurry solids from said slurry to a conveyor in the form 14 of a wet mat while draining the water therefrom, and rerucsirz'g residual moisture in the mat to form the fiberperlite board.

l0. II- method of forming a rapidiy dewatered in- 5 sulatien board, or the like of substantial thickness from an aqueous slurry which comprises making an aqueous slurry containing an amount not less than about 60% by weight of the soliu corstituents of the product of expander; :eriite, the partide size of which is [or th'ernost.

to part lessthan 20 mesh and s substantial proportion of which is as small as mesh or finer, and not less than about, by weiglt of short fiber whose fiber length is short enough to pe mit uniform dstrisutiun of the fiber throughout the man of perlite. and a small amount 15 of adhesive material, the soiids content of said slurry' being the approximate range of TIL-8% by weight,

agitating the slurry to eistribute said fibers uniformly thrcsghcut the slurry, transferring the slurry solids from said siurry to a conveyor n the form of a continuous wet mat and forming the solids thereof to such depth as to provide a product at least an inch in thickness, the per lite pertieies holding the fibers in separated condition and against segregation to maintain the free filtering chamcteristies of the perlite.

It. The trethod of rmnufacturing a fibrous pcrlitic board comprising the step; of forming a slurry of fiber, adhesive and water to a soiids consistency of approximately lf'e- 3% by wsight, r 'tiz'ng therewith expanded perlite particles to font: a new slurry having a solids content of app'oxim ttely 3'1-8'2 byweight. farming a wet mat of solids from the new slurry on said continuously moving foraminous surface, and drying the mat into n board.

12. The na-thod of manufacturing a fibrous perlitie board comprising the steps of forming a slurry consisting essenti slurry in whirlpool agitation while adding expanded perlitic partifles thereto to prevent the perlitic part cles from floating to the surface of the siurry, the total solids content of the slurry being approximately 392-856 by weight, forming a mat from the sfurry solids, and dr rg the formed mat to remove the residual moisture therefrom. l 3. 11:e method of manufacturing a fibrous perlitic board utilizing a continuously moving foraminous surface comprising the steps of forming a fibrous slurry, fonning a vortex of the slurry, adding to the slurry vortex expanded perlite particles so as to obtain proper intermixing of the ingredients, the solids content of the new slurry being in the approximate range of 3%8% by weigh and forming a board from the intermixed solids on said conzinuously moving foraminous surface.

14. The method of manufacturing a fibrous perlitic board comprising the steps of forming a slurry consisting essentially of fiber, adhesive. and water, adding expanded perlite particles to the slurry so as to produce a-solids content in the rangeof approximately 370-856 by weight, 4

said periite relative to the fibers being in the approximate range of 70-80 parts of perlite to 30-20 parts of fiber by weight, transferring the solids in said slurry to a continu- 00 otsly moving foraminous conveyor in the form of a mat while continuously draining the water therefrom, and drying the mat to remove most ofthe residual moisture contained in the board.

15. The method of manufacturing a fibrous perlitie board comprising the steps of forming a slurry consisting essentially of fiber, water, water repellent organic binder, and expanded perlite particles. said slurry having a solids content in the range of app aximately Bib-15% by weight, the perlite particles being of a nature such that most of the par icles pass a 20 mesh screen, depositing solids from the slurry upon a foraminous surface to form a wet mat thereon and drying the wet mat to remove excess residual moisture therein.

16. A method of producing an insulating board on a continuous basis utilizing a continuously moving forv of fiber, adhesive, and water, maintaining the foraminous surface, comprising the steps of V sluzry consisting essentially of fibers, expanded perlireforming 'ing a mesh screen, the fibers comprising apprcxirn aminous surface comprising the steps of forming a slurry consisting essentially of fibcrs. cz anded perlit: pznicies, tender and water, wherein the slurry has a sciiis content Wtlhin' the range of approximately 3-T' -S% by weight, forming a wet mat of solids from said ssrry on said continuously moving foraminous surface, and dewatering said wct mat.

17. A method of manufacturing an insulating lx ard on a continuous basis utilizing a continuous forzin'! a partic es, adhesive and water, the solids COntcfii of said slurry being within the approximate range of sea-srzby weight, said fibers compris'ng approximatcly SO'E-IO'I: by weight of the dry product. saic icrlite partie'es compzising approximately 402-80 '3 by weight of the dry product, amount,

and said adhesive being present in e'Z-eefive up to about by weight of the dry product, a wet net of solids, and dewatering said mat from said slurry on said continuously moving foraminous surface.

l8. An insulating material consisting' essertzially of approximately 4092-8096 by weight of c.\'p:tndtd erlite intertwined with a network of fiber, the expanded rerlite being capable, for the mo,t part, of passing a 20 mesh screen, the fibers comprising 505-1092 by weight of the product and being substantially uniformly disributed throughout the mass of per itc particles, and or Pic binder in effecti e amount, u; to approximately 25% by weight of the product, assisting to hold the perlite and 'fib cr in a relatively compact mass.

consisting of asphalt, resins, and starch.

20. An insulating material consisting essentially of approximately 6070-809: by weight of expanded perlite intertwined with a-network of fiber, the expanded parlite comprising a substantial portion of particles of approximately 100 mesh or finer, the fibers compilsing approximately %-15% by weight of the product and being substantia ly uniformly distributed through the mass of pcrlite particles, and water repellen: organic binder distributed in the mass and assisting to hold the perlite and fi'cer in a' relatively compact mass. 21. A thermal insulation consisting essentially of not ess than about 60% by weight of fine particles of expanded 'pcrlite of 20 mesh and finer particle s ze with a substantial portion as fine as 100 mesh or finer, said pezlite being held in the form of a substantially thick sheet by a network of fiber comprising not more than 505?: but

greater than 10% by weight of the dry ingred ents, the

fibers being substantially uniformly distributed in themass of perlite but-being too short ofthemselves to provide adequate strength, and a small but substantial amount,

not exceeding approximately 25% of the dry weight of the product of organic adhesive substance on the exterior surfaces of the fi'ecrs and perhte and assisting to hold the mass together.

- 22. An insulating material which is essentially ex panded perlite consisting essentially of very fine particles of expanded perlite held by a network of relatively short fibers substantially uniformly distributed throughout the mass of perlitc, the perlite having substantially none of the particles larger than 20 mesh and having a substantial portionas fine as mesh or finer, said perlite comprising not less than about 60% of the dry weight. of the pr duct, the fiber comprising approximately 35%-l5% of I the dry weight of the producL and said fibers and 'pcrlite having on their surfaces an effective amount, up to approximately 25? of organic adhesi e substance by weight,. as istng to hold theperlitc and fiber in a relatively compact mass.

23. An insulating material consisting essentially .of

comprising a substantial portion of fine grained particles of approximately 100 mesh and finer, the fibers comprising approximately 35%-l52 by weight of the product and being substantially uniformly distributed through the mass of perlitc particles, and organic binder distributed through and assisting to hold the perlite and fiber in a relatively compact mass;

24. A molded light weight insulating material, consisting essentially of particles of expanded perlite some of which are as fine rs 100 mesh in size, the perlite particles being in substantialcontact, sail con act being characterizcd by point contact as distinguished from surface contact thereby leaving a multitude of connecting interstices between the particles, and "t 'minor amount of short fiberiying n said interstices and constitutinga fiber network to hold said perlite in the molded shape, and an asphaltic binding constituent.

25. A molded light weight insulating material consisting essentially of particles of expanded perlite some of which are as fine as 100 mesh in size, the pcrlite particles being in substantial contact, said contact being characterizcd by point contact as distinguished from surface contact, thereby leaving a multitude of connecting interstices between the partic es, and a minor amount of short fiber lying in said interstices and constituting a fiber network to hold said rerlite in the molded shape, and a binding constituent consisting essential!" of organic material.

References Cited in the file of this patent UNITED STATES PATENTS Seybold Mar. 29, 1955 v